This invention relates to a phase detection circuit and to an automatic tint control circuit of a color television receiver.
The phase detection circuit forms an output in accordance with the difference between the phases (frequencies) of two input signals and is widely used for phase (frequency) control in television circuits. However, in performing phase control or the like, it is often desirable to restrict the control range.
Japanese Patent Laid-Open Specification No. 50-51626, for example, discloses an automatic tint control circuit which controls the phase of a reference color subcarrier signal applied to a color demodulator in order to reduce the variance of the relative phase difference between a chroma signal and a burst signal which may result from changes in the characteristics of a signal transmission line or may be due to the channel selection in the color television receiver.
In such an automatic tint control circuit, when the phase of a chroma signal of which the phase coincides with an I axis deviates for some reason or other by a quantity of phase difference .theta., for example, the phase of a reference color subcarrier signal to be applied to the color demodulator is corrected in accordance with the deviation quantity so that a correct tint is reproduced in the picture reproduced on the screen of the cathode ray tube (CRT). This phase correction of the reference color subcarrier signal is effected within the range of a limited deviation quantity in order to prevent the correction from being effected for all the deviation quantities and to prevent all the optional chroma signals from being processed as chroma signals having phases which coincide with the I axis.
In order to restrict the control range of the phase correction, in the above-mentioned automatic tint control circuit, there is provided a phase detection circuit in which chroma signals are impressed upon a first detector and a second detector, respectively; a first reference signal and a second reference signal, each having a different phase from the other, are impressed upon the first and second detectors, respectively; the output of the first detector is impressed upon a clipper; the output of this clipper and the output of the second detector are impressed upon a multiplier; and the output of this multiplier generates a control signal having a restricted phase range.